This invention relates to phytosterols and phytostanols, in particular to fatty acid esters of phytosterols and/or phytostanols with a specified fatty acid composition. The invention further relates to methods for preparation of the phytosterol and/or phytostanol esters and their uses.
Since the 1950""s numerous studies in animals and humans have been reported, in which plant sterols (phytosterols) have caused significant reductions in serum cholesterol levels. Plant sterols reduce serum cholesterol levels by reducing the absorption of cholesterol from the digestive tract. The mechanism or mechanisms by which this reduction in cholesterol absorption is taking place is not fully known.
Phytosterols are a group of compounds structurally very similar to cholesterol. The phytosterols occurring most frequently in the nature are sitosterol, campesterol and stigmasterol. In all phytosterol preparations is sitosterol the main component. Most clinical and non-clinical studies have been conducted with so-called tall oil sterols, containing high amounts of sitosterol and some sitostanol. In the scientific literature such sterol blends are often referred to as sitosterol. Vegetable oils and fats are the main source of plant sterols in our diet. In vegetable oils a major part of the sterols exists as fatty acid esters.
In earlier study""s plant sterols have been used in poorly soluble, crystalline form with high daily intakes (up to 20-30 g/day). However, even when administered in relatively small doses (a few grams per day) and under optimum conditions, plant sterols reduce serum total and LDL-cholesterol levels.
In recent years plant sterol treatment of hypercholesterolemia has been refined by the use of the fully saturated form of sitosterol, sitostanol. Saturated phytosterols such as sitostanol and campestanol are present in our diet in small amounts. Daily intake of total stanols in the Finnish diet has been estimated to 30-80 mg/day. However, tall oil sterols (sterols from pine trees) contain 10-20% of plant stanols (sitostanol+campestanol). Phytostanols can also be produced by hydrogenation to remove the double bond in corresponding plant sterols.
Sitostanol is virtually unabsorbed and lowers the cholesterol content of mixed micelles more efficiently than sitosterol, thus showing an enhanced serum cholesterol lowering effect. Sugano et al. (Sugano M,. Morioka H. and Ikeda I. (1977) J. Nutr. 107, 2011-019) showed that sitostanol had a higher hypocholesterolemic activity than sitosterol in rats. Similar results were obtained with rabbits (Ikeda I,. Kawasaki A,. Samazima K. and Sugano M. (1981). J. Nutr. Sci. Vitaminol. 27, 243-251). In addition, sitostanol depressed the formation of aortic atheroma due to cholesterol feeding more than did sitosterol. Becker et al. (Becker M,. Staab D. and von Bergmann K. (1993) Journal of Pediatrics, 122, 292-296.) showed, that sitostanol was significantly more effective than sitosterol in reducing elevated levels of LDL cholesterol in children with severe familial hypercholesterolemia.
The solubility of free sterol and especially of free stanol in edible oils and fats is very low. E.g. less than 2% free sterols are dissolvable in oils and fats if water is present. This problem can be overcomed by esterifying the free sterols with fatty acid esters. Esters of plant sterols have been shown to be equal to corresponding free sterols in reducing cholesterol absorption in rat (Mattson F. H., Volpenheim R. H. and Erickson B. A., (1977), J. Nutr. 107, 1139-46), while Mattson et al. (Mattson F. H., Grundy S. M. and Crouse J. R., (1982), Am. J. Clin. Nutr. 35, 697-700) found that free sterols were more effective in reducing cholesterol absorption in man.
During fat digestion dietary fat, sterol and/or stanol ester together with dietary cholesterol and its esters reach the intestinal oil phase (in intestinal emulsion), from which free stanols and sterols are released through lipolysis by enzymes like cholesterol esterase. The released free stanols and/or sterols compete with both dietary and biliary cholesterol for micellar solubility and lower the micellar phase concentration of cholesterol when present in lipid core fat material of the mixed micelles in high enough concentrations. Plant stanols like sitostanol is more effective in lowering micellar phase cholesterol than the corresponding sitosterol.
U.S. Pat. No. 3,751,569 (Erickson B. A.) describes clear cooking and salad oils having hypocholesterolemic properties. Into the liquid glyceride base oil is mixed 0.5-10 weight-% (as free sterol equivalent) of a sterol fatty acid ester. The cooking or salad oil was prepared by dissolving liquid glyceride base oil and plant sterols monocarboxylic acid in a mutual solvent and evaporating the solvent (hexane or diethyl ether). The fatty acid moiety was defined as a saturated mono-carboxylic acid C1-12 or an unsaturated fatty acid with up to 24 carbon atoms. The sterol ester is added in an amount small enough to prevent precipitation at refrigerating temperatures. The solubility of different fatty acid esters of phytosterol in triolein are also presented, showing very low solubility for C14 and C16 saturated fatty acid phytosterol esters. This patent discloses the use of certain individual fatty acid esters of phytosterols added to the cooking or salad oil in relatively small amounts.
Saturated plant sterols have been shown to be more effective in reducing the absorption of cholesterol from the digestive tract and thus causing enhanced reduction of total and LDL serum cholesterol levels. Saturation of plant sterols to plant stanols further decreases their solubility in oils and fats. U.S. Pat. No. 5,502,045 (Miettinen et al.) discloses a method for producing fatty acid esters of sitostanol and the use of the substance for lowering high cholesterol levels. By esterifying the sitostanol blend with fatty acids from a vegetable oil such as rapeseed oil (LEAR) a fat-soluble stanol ester was obtained. Examples are given showing that up to 20% of the normally used fat blend can be exchange with this sitostanol fatty acid ester blend based on low erucic acid rapeseed oil fatty acid esters. The incorporation of such fat-soluble stanol ester to food products like margarines and spreads provides a way to introduce the adequate daily amount of stanol for optimal reduction of the cholesterol absorption.
In several clinical studies these fat-soluble stanol esters have proven to be very effective in reducing the absorption of cholesterol from the digestive tract. The North Karelia stanol study was conducted to verify these findings in a 12 month large-scale randomised double-blind study (Miettinen T. A,. Puska P,. Gylling H,. Vanhanen H. and Vartiainen E. (1995). N. Engl. J. Med. 333, 1308-1312). The results from this study show that a daily intake of 1.8-2.6 g of fat-soluble sitostanol ester (calculated as free stanol) administered in a margarine decreased the total cholesterol with 10% and the LDL-cholesterol with 14% compared to the reference group having a margarine without added fat-soluble stanol ester.
Stanol fatty acid esters with fatty acids based on commercially available high PUFA vegetable oils such as sunflower oil, corn oil, soybean oil, safflower oil, cottonseed oil or their blends will show too high texturizing properties in vegetable oils or their blends in order to be incorporated into foods like salad oils, cooking oils, easily pourable salad dressings, sauces and mayonnaises in amounts high enough for an adequate daily intake of stanols and sterols in order to obtain an optimal cholesterol lowering effect. This problem will be solved by the present invention.
Another problem in the prior art is the production of food products with very high contents of phytosterols in a form that could be added to a variety of food products in concentration high enough to supply by normal food intake the daily adequate amount of sterols and/or stanol for optimum effect on blood cholesterol levels. This was partly solved in the prior art by producing the fatty acid esters of the phytosterols and phytostanols. However, by using the sterol and/or stanol fatty acid esters according to the present invention even higher amounts of phytosterols and phytostanols can successfully be used in certain vegetable oil based food products like salads oils, cooking oils, easily pourable salad dressings, sauces and mayonnaises.
Furthermore, sterol and/or stanol esters according to the current invention can successfully be used in spread type of products such as margarines, low-fat spreads, spreadable cheeses, butter etc., wherever there is a desire to use conventional triglyceride hardstock and not utilise the texturizing properties obtainable from sterol esters and/or stanol esters in the manufacturing of such products. One reason for such desire can be that utilising of sterol and/or stanol esters according to the present invention is technically not so demanding, making it more easy and feasible to produce such products with conventional production technology.
Capsules with free sterols and stanols suspended in safflower oil or mono-olein have been used as a mean for lowering elevated cholesterol levels. E.g. Denke (Denke (1995) Am. J. Clin. Nutr. 61, 392-396) fed 4 capsules/meal of free stanol suspended in safflower oil to men with moderate hypercholesterolemia as part of a cholesterol-lowering diet. The total daily intake of sitostanol was 3000 mg provided in 12 capsules. The sitostanol capsule regimen did not significantly reduce LDL cholesterol levels compared to the diet alone.
Due to the low solubility of free sitostanol in vegetable oils the use of capsules containing free sitostanol suspended in safflower oil does not ensure that the sitostanol is efficiently distributed into the fat phase of the food digest. This problem can be overcomed by using capsules based on sterol and/or stanol esters according to the present invention, since these esters are liquid at body temperature and will easily be dissolved into the fat phase of the food digest. In addition no triglyceride fat or mono-olein is needed as a dispersing agent, making it possible to reduce the size or amount of capsules needed to supply the daily needed optimal amount of sterols and/or stanols.
The present invention is based on the finding that sterol and/or stanol fatty acid ester compositions, in which more than 50% of the fatty acid moieties comprises polyunsaturated fatty acids (PUFA), preferentially more than 60% and more preferred more than 65%, and less than 7% comprises saturated fatty acids (SAFA), preferentially less than 5%, show basically no texturizing properties and can thus be used in food products were such a texturizing effect is due to product quality or production technology reason undesirable or is wanted only to a very limited degree.
The invention is further based on the fact that stanol fatty acid esters based on rapeseed oil with a low content of saturated fatty acids and a high content of unsaturated fatty acids (mainly monounsaturated) give a DSC melting curve (FIG. 1), where all stanol fatty acid esters have co-crystallized. Thus, this blend of stanol fatty acid esters melts in one distinct melting peak measured with differential scanning calorimetry (DSC) after a directed crystallisation procedure. The DSC melting curve is obtained after melting the sample (about 8 mg) at 75xc2x0 C. for 10 minutes, after which the sample is crysallised by cooling at 10xc2x0 C./minute to xe2x88x9250xc2x0 C., where it is kept for five minutes. The melting curve is obtained by heating at 10xc2x0 C./minute to 70xc2x0 C.